1. Field of the Invention
The present invention relates to, for example, an image forming system in which a plurality of types of recording media can be used, and, in particular, to a detector for detecting recording medium.
2. Related Background Art
FIG. 7 is a schematic diagram illustrating the general operation of an image forming system, in which reference numeral 101 denotes a recording medium (such as paper) onto which is formed an image; reference numeral 102 denotes a platen; reference numeral 103 denotes a recording head; reference numeral 104 denotes a paper width sensor; reference numeral 105 denotes sub-scanning rollers; and reference numeral 106 denotes discharge rollers.
The paper width sensor 104 is mounted to the recording head 103 with high precision. Allowing the recording head 103 to scan as during recording operation makes it possible for the paper width sensor 104 to read the state of the platen 102 or the recording medium 101.
FIG. 8 is a detailed view of the paper width sensor 104.
The paper width sensor 104 is the so-called reflection-type sensor, in which light emitted from light-emitting section 141 is reflected by the platen 102 (or the recording medium 101), and the reflected light is detected by a light-receiving section 142 to generate a voltage in accordance with the amount of reflected light.
In preparing for recording, the recording medium 101 is fed to the gap between the sub-scanning rollers 105 by a feeding means (not illustrated). When it reaches the gap, the sub-scanning rollers 105 rotate to transport the recording medium 101 on the platen 102 to the gap between the discharge rollers 106. When it reaches the gap, the discharge rollers 106 rotate to allow the recording medium 101 to be in a uniformly stretched state on the platen 102.
In general, the platen 102 is positioned higher than the line formed by connecting the gap between the sub-scanning rollers 105 and the gap connecting the discharge rollers 106. In addition, the pressure applied by the discharge rollers 106 is low. These rollers are designed so that they convey more recording media than the sub-scanning rollers 105 per unit time, and, as described above, puts the recording medium 101 under tension.
Thereafter, the paper width sensor 104 scans the recording medium 101 to determine the position and type of the recording medium, after which the recording range, image parameter, etc., are set. This completes the preparation for recording.
The types of recording medium 101 used include OHP sheets used for OHP in addition to the ordinarily used paper (hereinafter simply referred to as paper).
The position and type of paper is determined in the following way.
For ordinary paper, the paper width sense data at position x is compared with the threshold value T to determine the position (size) of the paper. An error is said to occur if paper could not be detected due to, for example, paper misfeeding.
For OHP sheets, an error is said to occur when the fed sheets are not detected.
When OHP sheets are used, the operator inputs that the recording media used are OHP sheets by means of operation section.
When the paper width sensor detects the presence of paper, the recording media used are not OHP sheets. This is defined as an error.
However, in the above-described conventional example, the operator must give an instruction to determine the type of recording medium 101 used, such as, for example, whether the medium type used is ordinary paper or an OHP sheet. In such a case, the operator may forget to make specifications or make operational errors which result in malfunctioning. In addition, a plurality of paper types, including OHP sheets, cannot be correctly distinguished automatically even if this was attempted due to, for example, dirty platen or changes in platen density with the passage of time.